swap pager:indefinite wait buffer: message out of vm.c

Benjamin Lee ben at b1c1l1.com
Thu Dec 2 22:04:47 UTC 2010

On 12/01/2010 03:23 PM, Mark Terribile wrote:
> Hi,
> Would some kind soul please tell me the meaning of a message coming
> from vm.c (FreeBSD 7.2):
> "swap pager: indefinite wait buffer: bufobj: 0, blkno: 2, size: 4096"
> This message occurs after a return from an msleep whose last args are PSWP,
> "swread", and HZ*20 .
> When it occurs, some interactive program is locked up.  It recovers
> sometime later.
> My best guess is that this is a complaint that swap or paging I/O has been
> excessively delayed.  It is occurring while I am running disk-to-disk
> transfers that have deep buffering.  Think mbuf(1), but it's my own code,
> testing some algorithms.  I speculate that if the disk queuing/head movement optimization doesn't let the heads move off the file system
> where the file resides (and I only see this with large, single files)
> then this problem might result.  But that is a guess, and speculation.
> Does anyone know if this can occur under later versions of FreeBSD?

Hi Mark,

Do you have any test cases that reliably reproduce the problem?  I've
seen it crop up very infrequently on 8.1-RELEASE but I haven't been able
to reproduce it.

Benjamin Lee

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